Agressive groumies?

Question
I gave up my love for groumies because after a few months they would become aggressive.  Lots of chasing other fish and in two completely separate occasions in different tanks, where (seemingly! I was only 10 mind you), the most aggressive fish killed a few others.  I would suppose by simply harassing them to death!  Now I don't know if maybe they were old, or sensitive and the PH wasn't right.  I would have chalked it up to an unknown disease or bad PH levels, but I had the largest, most aggressive fish left, unscathed, and my other fish (and tank) had seemed completely healthy.  So, is this behavior normal for groumies or is there something that can trigger this kind of behavior?  All I've ever heard of Groumies is how peaceful they are.  I would love to have more, but I'm afraid the same thing will happen.  
P.S.-Sorry if this question was too long!

Answer
Hi Sarah;

Gouramis can be very territorial and aggressive for sure. It's mostly the males. Especially in small tanks. The more room they get and the more hiding places there are, the better the other fish can cope with the gouramis. Gouramis are in the same family as the Siamese Fighting Fish, more commonly known as the Betta. Bettas are territorial with their own kind, that's why they have to be kept from other males.

At Your Service;
Chris Robbins